Mine accident investigation statistics reveal that a surprisingly large number of fatal accidents occur every year through unpredictable roof falls, even in mines where all presently applicable safety regulations stipulated by the law are rigidly and meticulously enforced. Such accidents are routinely classified as "Act of God" because heretofore there has been no way for mining safety engineers to detect and monitor the development of dangerous, unstable rock conditions underground. Heretofore, the only methods to check the roof conditions have been (a) observation of the tensile strength increment on the rock bolts which indicates stress build-up in the roof and (b) "sounding" the rock by tapping it with a scaling bar. It will be appreciated, however, that neither of these methods is infallible because (a) tensile stress build-up may not occur because the rock bolts themselves may move with the sagging rock block and (b) the developed separations are initially very small and can be located very deeply within the rock mass so that tapping will fail to reveal any unsoundness.